The present invention relates to an innovative system comprising a tightening tool such as a microprocessor-controlled torque wrench and a tool-data processing terminal.
Torque wrenches or torque-controlled screwers are tools used in mass production and assembly lines to ensure that screws and nuts are tightened to the correct torque to achieve the desired preloading in the connection to ensure sufficient friction under the head to avoid screw loosening.
To be sure that a given screw has really been tightened, torque wrenches communicating completed tightening to an external monitoring system have been developed. Initially cable communication systems were proposed but the existence of a connecting cable limits the operator""s freedom of movement and is often a source of failure. Therefore torque wrenches which communicate completed tightening by radio were developed.
Radio transmission is preferred by the operator but has as its main defect the poor reliability typical of radio transmissions. Indeed, all radio systems used in industry must work in a narrow frequency band, the number of available channels is limited and the possibility of interference is considerable. It is also extremely difficult to limit the radio range to the distance actually necessary e.g. one meter and no more and even a distant but strong signal can interfere with transmission. All this makes operating with a relatively high number of wrenches in a restricted area extremely complicated.
Because of the above mentioned limitations radio systems are employed in practice only for transmission of the wrench click when it occurs so as to count how many clicks have occurred.
In many cases today electronic torque wrenches with digital reading are used both for their high torque measurement accuracy and for their ability to memorize the values read to later transfer them to computer systems for data processing. This way it is possible to control the correctness of the tightening values a posteriori e.g. by connection with a cable via RS232 but it is not possible to be sure that a given tightening in a specific position was actually performed by the operator. To meet these requirements it is therefore necessary to connect the torque wrench to an external monitoring system which verifies correct operation performance in real time, memorizing the data related to the operation performed and previously programmed on the monitoring system. The monitoring system can then allow subsequent operations if the congruousness of the preceding operation is verified. Connection between the wrench and the monitoring system could benefit by radio transmission but the above mentioned shortcomings advise against such a solution.
Another complication is met with if two-way communication is necessary e.g. if tightening parameters change with the screw to be tightened and are known to the system but not to the wrench. On the one hand the system must communicate to the wrench the correct tightening parameters for a given screw and on the other hand the wrench must communicate not only that the tightening was performed correctly but the torque value achieved. In addition the data (torque) must be associated in real time with the position where the wrench is operating. It is clear that with such transmission complexity and with the necessity that the communication take place in real time and with no possibility of interference the radio system does not offer sufficient reliability assurance.
The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a tightening tool and monitoring station which would communicate wirelessly with each other while avoiding interference and with the addition advantageously of identification and position information.
In view of this purpose it was sought to provide in accordance with the present invention a portable tightening tool and a monitoring and control station for this tool in which the tool comprises in combination a microprocessor unit for management and measurement of tool operation parameters and a transponder unit for communication with the monitoring station and equipped in turn with at least one decoder for communication with the transponder with the microprocessor unit receiving tightening parameters from the station through the transponder and sending to the station through the transponder measurements taken by the tool.